Anode assembly for mercury cathode cells



l July 12, 1966 G. P. HENEGAR ANODE ASSEMBLY FOR MERCURY CATHODE CELLS Filed Feb. 13, 1962 .IP 6 INVENTOR:

/ff;-f. GLEN E HENEGAR #i /U/l ZE BY IIE [F116 5 AGENT the joints between United States Patent() 3,260,662 ANODE ASSEMBLY FOR MERCURY CATHODE CELLS Glen P. Henegar, Saltville, Va., assignor to Olin Mathieson Chemical Corporation, a corporation of Virginia Filed Feb. 13, 1962, Ser. No. 173,070 6 Claims. (Cl. 204-279) This invention relates to electrolytic alkali-chlorine cells of the mercury cathode type. More particularly the invention relates to an improved structure for supporting the anode and for protecting the lead-in from the cor-rosive action of cell gases. l

Anodes are conventionally suspended in the electrolyzer chamber of mercury cells by means permitting adjustment of the elevation of the anodes with respect to the bottom of the cell and the mercury cathode owing thereon. The lead-in serves to conduct the electric current from outside the cell, usually from a bus bar, to the anode inside the cell. The lead-in also usually serves to support the anode and is appropriately threaded or otherwise designed to permit frequent and close adjustment of the elevation of the anode.

Various materials have been used for lead-in structures but the primary considerations are cost, structural strength and high electrical conductivity. Cupreous metals, including particularly copper and brass, are particularly preferred as lead-in materials satisfying these three p-rimary requirements. However, copper and brass are rapidly attacked by the moist chlorine gas inside the cell and must be protected therefrom. U.S. Patent 2,328,- 665 refers to an insulator sleeve around that portion of the lead-in which passes through the aperture in the cover primarily to avoid electrical contact of the leadin with other structures. U.S. Patent 2,627,501 describes a porcelain pipe concentrically around the lead-in to seal off the lead-in from contact with anode gases and the electrolyte. Porcelain sleeves suffer from the defect of fragility and are likely to crack in use partly due to uneven heating and partly to attempts to tighten the joints at the upper and lower ends of the sleeve to avoid gas leakage.

` In prior structures the weight of the anode is carried by the lead-in which has been attached by various means to the anode. Under the severe service conditions in mercury cells in the presence of elevated temperatures, water and water vapor, chlorine and hydrochloric acid gas, the joint between the lead-in and the anode is a frequent source of mechanical failure, allowing the anode to incline or drop to the bottom of the cell, or electrical failure, developing increased resistance across the joint or permitting short circuits if the anode contacts the mercury cathode. The sleeves of the prior art have aggravated these diculties by increasing the mechanical pressure on the anode lead-in joint in attempts to effect a gas-tight seal of the sleeve against the anode. The sleeve of the present invention, in contrast, effects the complete protection of the lead-in from the action of cellgases, contributes to the support of the anode instead of aggravating the problem, and eliminates at least one of the lead-in and the graphite anode. Advantageously, the graphite anodes are impregnated with oil -in the vicinity of the lead-in joint to render the anodes impervious to chlorine and to prevent its deleterious action on graphite threads.

3,260,662 Patented July 12, 1966 ice The titanium sleeves of the present invention are fabricated in a manner which has the advantage of avoiding the necessity for a seal between the lead-in and the upper end of the sleeve and also avoiding the necessity for a lead button or other means of contact between the leadin and the graphite anode. It co-operates with the leadin to support the anode in the cell and provides better electrical contact while eliminating one cause of electrical and mechanical failure, namely, the usual lead button.

The sleeve of the present invention comprises a titanium tube with thick Walls near one end and closed at that end by a flat button of titanium. The thick walled portion of the sleeve is a minor proportion of the total length of the sleeve and may be, for example, from about 1/2 to l1/2 inches in a total length of 3 to 8 inches. The thin walled portion of the sleeve is appropriately fabricated of titanium tubes'of any appropriate diameter t0 accommodate the lead-in leaving a concentric air space between the two. The ai-r space usually amounts to about 1/16 to 3%; inch. Tubing of 1/16, to 3/32, or 1/8 inch in wall thickness are commercially available and suitable for this purpose. The walls of the tubing may be thickened at one end by mechanical working, closed by means of a hat sheet of titanium welded onto the thickened walls and machined as described below. Alternatively and preferably, the thick walled portion of the sleeve is fabricated from a section of tubing having thicker walls and smaller internal diameter than the thin walled portion of the sleeve. end by welding thereto a disc of titanium, machining the inner and outer walls and welding the thicker walled section to the thinner walled section. In another mode, the thick walled section may be fabricated from a solid billet of titanium, removing most of the center portion to form a cup having a bottom and side walls, forming the inner and outer walls of the cup to receive the lead-in and to engage the anode, respectively.

The inside diameter of the thick walled portion of the sleeve is less than that of the thin walled portion of the sleeve in order to assemble the post by sliding the sleeve over the lead-in until the inner surface of the thick walled portion engages the lead-in. The inner wall of the thick wall portion of the sleeve is machined to provide for press litting or interference fitting the lead-in into the thick wall portion. Alternatively the thick wall portion of the sleeve and the lower end of the lead-in are threaded and thus tightly engaged. The outer surface of the thick walled portion of the sleeve is machined for press -litting or interference fitting into a recess in the graphite anode or is threaded into a correspondingly threaded recess in the graphite anode. The lead-in is completely enclosed `by the titanium sleeve eX- cept that the lead-in protrudes from the top and the assembly is supported by threads clamps or in any conventional manner.

Improved electrical contact can be obtained, if desired, by modifying the shape of the inserted end of the lead-in and of the closed end of the sleeve to provide a stub of reduced diameter on both the lead-in and the bottom of the sleeve. When the lead-in is threaded into the sleeve and the sleeve in turn is threaded into the recess in the graphite anode, larger areas of contact are provided for electrical conductance.

The titanium sleeves have the advantage over porcelain or alumina that they will not crack, they are The heavier tubing is closed at one not sensitive to temperature changes and they can readily be fabricated with the necessary precision. They are superior to other metal sleeves in their complete resistance to any action by wet chlorine gas. Compared to plastic materials they do not creep or flow. Where there is any possibility of contact with cell gases with the lead-in it is completely protected by titanium since the lower end of the sleeve is -capped by titanium.

While the above description refers particularly to titanium, it is to be understood that tantalum is equally satisfactory for fabrication of the protective sleeves of the present invention. Tantalurn suffers mainly from its present high cost. Alloys in which titanium or tantalum are the principal constitutents are also useful, including titanium silicide, TiSi2 in which the titanium amounts to a little more than 45 percent. Generally titanium, tantalum and alloys in which they are the principal constituents and which exhibit corrosion resistant properties comparable to titanium and tantalum in the environment of the present invention are suitable.

Graphite anodes are conventional in the art and the present invention is admirably adapted thereto. However, the invention is not limited thereto and is also useful with anodes of other suitable materials, including metals, particularly platinum, titanium, tantalum and platinized titanium, for example.

Attached FIGURE 1 shows an anode assembly of the present invention in which the lead-in is interference tted into the sleeve and the sleeve in turn is interference fitted into the graphite anode. The sleeve consists of bottom 11A, thick walled portion 12A, and thin walled portion 13A. Lead-in 21A is concentrically interference fitted into portion 12A until it contacts bottom 11A of the sleeve. The thin walled part 13A has a slightly greater internal diameter than that of the thick walled portion 12A. The assembled lead-in 21A and sleeve is interference fitted into the recess in graphite anode 14A. The oil impregnated portion of the anode is indicated at 20A. A flexible rubber boot 15A is attached to cell cover 16A and, by means of clamp 17A, tightened by screw 18A to the upper portion of the sleeve.

FIGURE 2 shows a modification in which lead-in 21B is interference tted into the thick walled portion 12B of the sleeve having thin walled portion 13B. 'Ihe thick walled portion 12B is externally threaded and screwed into a correspondingly threaded recess in anode 14B. The bottom 11B of the sleeve does not quite contact the bottom of the recess in anode 14B.

FIGURE 3 shows a modification in which lead-in 21C is threaded into the internally threaded thick walled portion 12C. The thick walled portion 12C is externally machined for interference fitting into a recess in anode 14C. The bottom of the sleeve is indicated at 11C and the thin walled portion at 13C.

FIGURE 4 shows a modification in which the thick walled portion 12D of the sleeve is threaded internally and externally to receive correspondingly threaded leadin 21D and to screw into a correspondingly threaded recess in anode 14D. The bottom of the sleeve is shown at 11D and the thin walled portion at 13D.

FIGURE 5 adds a ange 19E to the thick walled portion 12E of sleeve. The thick walled portion 12E is externally threaded to fit a correspondingly threaded recess in anode 14E. Lead-in 21E is interference fitted into the thick walled portion 12E. The bottom of the sleeve is shown at 11E and the thin walled portion at 13E. The anode is shown at 14E. The flange 19E provides added protection and strength to the threads.

FIGURE 6 shows a modification in which a stub 22F of reduced diameter is provided at the end of the lead-in 21F and the bottom of the sleeve 11F has a stub of reduced diameter. When the threaded lead-in is tightened into threaded thick walled portion 12F of the sleeve, stub 22F is brought into good electrical contact with lbottom 11F of the sleeve. Similarly when the threaded thick walled portion 12F of the sleeve is tightened into threaded recess in graphite anode 14E, bottom 11F is brought into good electrical contact with the graphite. The thin walled portion of the sleeve is shown at 13F.

Example I Anode assemblies were fabricated in the style of FIG- URE 2. For the thin Walled portion, titanium tube having an outside diameter of 2% inches with a wall thickness of %2 inch was used. To one end of each tube was welded a section of titanium tube having an outside diameter of 2.1/2 inches. This thick walled portion was closed by welding a circular plate of titanium ls inch thick to the open end of the larger tube. The thick walled portion was externally threaded to fit a correspondingly threaded recess in graphite anodes 16l X 16 X 6 inches. Brass pipe, 1% inches in diameter was intereference fitted under 5,000 p.s.i. pressure into the inside of the thick walled portion which had an inside diameter 0.006- inch less than the brass pipe. The anode post assemblies were fitted with flexible boots and suspended in operating mercury cells. In operation, including regular adjustment of the interelectrode distances, the titanium sleeves and brass lead-ins were completely unattacked. None of the anodes were lost by dropping to the bottom of the cell and none were tilted or short-circuited by shifting at the anode-lead-in joint.

Example 1I Several titanium sleeves of the style of FIGURE 4 were fabricated of titanium tube having an outside diameter of 21A inches with a wall thickness of 3/32 inch. To one end of each tube was welded a titanium cup turned from a solid billet of titanium having a diameter of 21/2 inches. The center was cut out leaving a cup having a bottom I; inch thick and a wall which, when internally threaded, fit corresponding threads on 1% inch brass pipe. The thick walled portion was externally threaded to fit a correspondingly threaded, oil impregnated recess in a graphite anode. The anode post assemblies were lfitted with flexible boots and suspended in operating mercury cells. Each titanium-to-graphite joint carried a current of approximately 1000 amperes. The voltage drop across the joint varied as follows:

Time, days: Voltage drop `Original 0.000222 y67 .001130 98 .001180 133 .000986 162 .001000 After the initial change, no further increase in voltage appeared during this test. This stability compares favorably with the steadily increasing voltage drop frequently found with other joints.

What is claimed is:

1. An anode assembly for mercury cells comprising a graphite anode having a cylindrical recess in its upper surface, a cupreous metal lead-in and a tubular sleeve surrounding the lead-in, said tubular sleeve having a thin walled portion and, near one end, a thick walled portion of smaller internal diameter than the thin walled portion, said sleeve open at the end having the thin walled portion and closed by a at bottom at the end having the thick walled portion, said lead-in fitted internally into the thick walled portion with clearance between said leadin and the thin walled portion of the sleeve, said thick walled portion tted internally into the recess in said anode, said tubular sleeve composed of a metal selected from the group consisting of titanium, tantalum and alloys in which said metals are the principal constituents and which exhibit corrosion resistant properties comparable to titanium and tantalum.

2. The anode assembly of claim 1 in which the thick walled portion of the sleeve is internally threaded to receive corresponding threads on the lead-iu.

3. The anode assembly of claim 1 in which the thick walled portion of the sleeve is externally threaded to engage corresponding threads in the recess in the anode.

4. The anode assembly of claim 1 in which the thick walled portion of the sleeve is internally adapted to receive the lead-in by interference fitting and externally lthreaded to engage corresponding threads in the recess in the anode.

5. The anode assembly of claim 1 in which the sleeve additonally has an external flange perpendicular to the axis of the sleeve at the junction of the thick walled portion and the thin walled portion of said sleeve.

6. The anode assembly of claim 1 in which the sleeve is composed of titanium.

References Cited by the Examiner UNITED STATES PATENTS 2,328,66-5 9/ 1943 Munson 204-286 2,986,513 5/1961 Ornhjelm 204--286 3,037,928 6/1962 Hass 204--286 3,080,310 3/1963 Lindenmaier 204-286 FOREIGN PATENTS 616,029 3/1961 Canada.

124,423)l 11/1958 U.S.S.R.

JOHN H. MACK, Primary Examiner.

D. R. JORDAN, Assistant Examiner. 

1. AN ANODE ASSEMBLY FOR MERCURY CELLS COMPRISING A GRAPHITE ANODE HAVING A CYLINDRICAL RECESS IN ITS UPPER SURFACE, A CUPREOUS METAL LEAD-IN AND A TUBULAR SLEEVE SURROUNDING THE LEAD:IN, SAID TUBULAR SLEEVE HAVING A THIN WALLED PORTION AND, NEAR ONE END, A THICK WALLED PORTION OF SMALLER INTERNAL DIAMETER THAN THE THIN WALLED PORTION, SAID SLEEVE OPEN AT THE END HAVING THE THIN WALLED PORTION AND CLOSED BY A FLAT BOTTOM AT THE END HAVING THE THICK WALLED PORTION, SAID LEAD-IN FITTED INTERNALLY INTO THE THICK WALLED PORTION WITH CLEARANCE BETWEEN SAID LEADIN AND THE THIN WALLED PORTION OF THE SLEEVE, SAID THICK 